8 Muscles Physiology: MUSCLE STRUCTURE SLIDING FILAMENT THEORY (or, 6[ish] easy steps to contraction) 3 TESTS OF THE SLIDING FILAMENT MODEL Where hath all my skin gone? 1
8 Muscles Physiology: MUSCLE STRUCTURE
SLIDING FILAMENT THEORY
(or, 6[ish] easy steps to contraction)
3 TESTS OF THE SLIDING FILAMENT MODEL
Where hath all my skin
gone?
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Weekly Quiz 2: regrade Q4
Review session: Tomorrow, 5:00 or 6:00?
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Striated muscle fibrils
fiber
fibril
sarcoplasmic reticulum in x-section
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Myofilament organization dictates the macroscopic appearance of muscle.
A = dark
I =
light
Z disc
Q: through which parts of the fiber were these sections made?
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The Sliding Filament Theory of muscle contraction
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The neuromuscular junction is the point of synaptic contact between the axon terminal of a motor neuron and the muscle fiber it controls.
Action potentials in the motor neuron cause acetylcholine release into the neuromuscular junction.
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DHP “receptor” senses t-tubule voltage->ryanodine receptor
Q: Where in the muscle contraction cycle do ligand-gated channels occur? Voltage-gated?
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ryanodine receptor releases Ca2+ into cytosol.
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Ryanodine
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Relaxed: tropomyosin blocks the cross-bridge binding site on actin.
5 Ready: Ca2+ binds to troponin: -tropomyosin “moves” -myosin binding sites exposed.
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6 another 6 substeps involving ATP hydrolyzation
6.1
6.2
6.3
6.4
6.5
6.5
A-M binding, ready
ATP binds to actin, release A-M bond
ATP partially hydrolysis
Actin head “cocked”
“power stroke” powered by P release
ADP released, binding site clear
at rest
THREE TESTS OF THE SLIDING FILAMENT MODEL Q: Do sarcomeres change in length and structure when they contract? If so, which regions contract?
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at rest
contracted
THREE TESTS OF THE SLIDING FILAMENT MODEL Q: Do sarcomeres change in length and structure when they contract? If so, which regions contract?
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Furaptra = a fluorescent calcium indicator
Q: Does concentration of myoplasmic free calcium change during contraction?
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Furaptra = a fluorescent calcium indicator
Q: What is happening between the time of the action potential and the peak of myoplasmic calcium?
Q: Why is the contractile force generated AFTER the spike in myoplasmic free calcium?
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Q: Does the force generated by muscles differ in muscles of different resting length?
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HINT: ARE FILAMENTS INFINITELY LONG?
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Q: Are all contractions functionally similar?Q: Which ones make you most sore?
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Q. How do muscles generate variable amounts of tension?
CONTRACTION ENERGETICS
Slow oxidative (SO),
fast glycolytic (FG), and
fast oxidative glycolytic (FOG)
fibers have distinctive traits visible even in histologic section
Three metabolic pathways supply ATP for muscle contraction
Q: How might dominant fiber type differ among athletes with different specialties?
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Proportion SO vs FG up to 83% of vastus lateralis fibers are FOG and FG (PK = pyruvate kinase / LDH = lactate dehydrogenase)
Glycolytic enzymes PK and LDH levels are elevated CS = citrate synthase / HOAD = 3-hydroxyactyl-CoA dehydrogenase Oxidative enzymes CS and HOAD levels are depressed
Mitochondria 2-4% of volume of muscle fiber
Myoglobin concentration within range of other sprinters and endurance runners
Fiber types in the running muscles of the cheetah (Williams et al. 1997)
MUSCLE CELL TRADE-OFFS
Q: Is there a downside to being the fastest mammal? http://www.youtube.com/watch?v=jMwefq1ZtNI
Muscle cell volume as a zero-sum system
From: Rome and Lindstedt. 1998. News Physiol. Sci 13:261-268.
Q: Predict the effects of maximizing:
muscle protein
mitochondria
sarcoplasmic reticulum
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If cell volume is constant, tradeoffs exist.
Mitochondria(“fuel tank”)
Myofibrillar(“horse power”)
Sarcoplasmicreticulum
(“accelerator”)
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Q. How does Ca2+ get back within SR?
sarco/endoplasmic reticulum calcium-ATPase (SERCA) actively pumps calcium back into the SR
Calcium transients for three different fibers taken from the oyster toadfish. SO fibers FG fibers Superfast twitch swimbladder fibers
Q: which is which? Q: what can you predict about cell composition?
seconds
http://www.dosits.org/audio/fishes/oystertoadfish/
≈ 90 ≈ 5 ≈ 5
50 30 4
31 26 26
myofibrils SR mitochondria (force) (Ca++ uptake) (ATP supply)
Q: Which of the muscle profiles belongs to each of the muscles pictured?
toadfish swim bladder typical skeletal muscle rattlesnake rattle
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8.5 - Food and Fuel
Hydrolysis vs. cellular respiration
Digestive tract anatomy and function
Feeding
Mechanical breakdown
Storage
Chemical breakdown = hydrolysis
Absorption of monomers
(elimination)
DIGESTIVE TRACT ANATOMY AND FUNCTION
Transported and assembled into more complex molecules after absorption
HEADGUT - food capture, reception, mechanical breakdown, some storage (usually mouth, teeth, lips, tongue, salivary glands)
FOREGUT - food conduction, storage, chemical digestion, limited maceration (usually esophagus and stomach)
MIDGUT - chemical digestion and absorption (usually small intestine)
HINDGUT - water and mineral absorption, waste storage and elimination (usually large intestine / rectum)
Sequential processing of food
Examples of EXOCRINE processes in digestion (monomers of macromolecules)
bile is an emulsifier (not an enzyme)
pepsin, a protease
salivary amylase, a carbohydrase
bicarbonate adjusts pH (not an enzyme)
lipases, carbohydrases, and proteases make up “pancreatic juice”
Examples of ENDOCRINE processes in digestion.
secretin stimulates pancreatic release of bicarbonate
cholecystokinin simulates release of pancreatic enzymes (and bile)
gastrin stimulates pepsinogen and acid release
Review: glucose homeostasis is regulated (in part) by pancreatic hormones
If blood glucose is high…..
If blood glucose is low …
α-cells are red
β-cells are blue
Q: How can external conditions affect glucose levels?
The HPA axis
CRH = corticotropin releasing hormone
ACTH = adrenocorticotropic hormone
Glucocorticoids (e.g. cortisol, corticosterone)
CARNIVORY vs HERBIVORY
Q: Which diet is “higher quality” – carnivorous or herbivorous ?
Hume, 1989
Slicing dentition
Small stomach
Short midgut
Large liver (bile production)
Little storage space
Short transit time
Q: What makes meat so easy to digest? Q: How is diet reflected in digestive tract anatomy?
Carnivores
QQ1: What is so problematic about a plant diet?
Q: What digestive strategies are available to overcome these difficulties?
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